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An object of mass m is tied to a string of length L and a variable horizontal force is applied on it which starts at zero and gradually increases until the string makes an angle Theta with the vertical. The work done by the force F is mgL(1-sin(th)) mgL mgL(1-cos(th)) mgL(1+cos(th)) I got the answer as mgL(1-cos(th)).. but the answer is given mgL(1+cos(th)). I am confused, please explain the answer

An object of mass m is tied to a string of length L and a variable horizontal force is applied on it which starts at zero and gradually increases until the string makes an angle Theta with the vertical. The work done by the force F is
  1. mgL(1-sin(th))
  2. mgL
  3. mgL(1-cos(th))
  4. mgL(1+cos(th))
I got the answer as mgL(1-cos(th)).. but the answer is given mgL(1+cos(th)). I am confused, please explain the answer

Grade:12

2 Answers

Swagat Bordoloi
37 Points
9 years ago
any one help please.
Mallikarjun Maram
50 Points
9 years ago
Your answer is correct.  From work energy theorem, since change in Kinetic energy is zero, the total work done by all forces must be equal to zero.
That means, WF + Wg = 0
WF = –Wg = mgL(1 – cos theta)

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